Method for producing welded tubes from steel

Abstract

In a method for producing welded pipes from steel, in which strips or metal sheets are formed into a pipe provided with a longitudinal or helical slot and the abutting edges of the slotted pipe are welded together, the process parameters for production of the pipes are specified on the basis of previously ascertained material properties and geometry of the strips or metal sheets. Before the forming process, the strip or metal sheet is subjected to an nondestructive, continuous or discontinuous test for inhomogeneities over the length and width, an integral characteristic value for the material property of the strip or metal sheet is formed from the measured values, a measure of the homogeneity of the material properties relating to the length and width of the strip or metal sheet is derived from the variance in the measured values for the various measurement points and, in the event of deviations in the measured values exceeding previously specified limit values, the process parameters are reset and/or the strip or metal sheet is subjected to a homogenisation process prior to the forming process.

What is claimed is:  
     
       1. A method for producing welded tubes from steel, comprising:
 obtaining measuring values regarding material properties of a strip or metal sheet at different measuring sites along a length and width of the strip or metal sheet by a nondestructive continuous or discontinuous testing; 
 forming an integral characteristic value for the material properties of the strip or the metal sheet as a function of the obtained measuring; 
 determining a degree of homogeneity of the material properties with regard to the length and width of the strip or metal sheet as a function of a variance of the measuring values at the different measuring sites; 
 when a deviation of the measuring values exceeds a predetermined threshold, adjusting process parameters used for producing the welded tubes and/or subjecting the strip or metal sheet to a homogenization process; 
 applying the adjusted process parameters during forming of the strip or metal sheet into a longitudinal or helical open seam tube and during welding of confronting edges of the longitudinal or helical open seam tube. 
 
     
     
       2. The method of  claim 1 , wherein the nondestructive testing comprises introducing ultrasound into the strip or metal sheet and measuring a runtime of the ultrasound, said variance of the measuring values being commensurate with a difference in runtimes of the ultrasound. 
     
     
       3. The method of  claim 2 , wherein at least two independent ultrasound modes are used for the testing, said method further comprising correlating runtimes of the two independent ultrasound modes with each other to thereby eliminate an influence of a respective thickness of the or strip or metal sheet. 
     
     
       4. The method of  claim 3 , wherein transverse waves with different polarization direction are used as ultrasound modes. 
     
     
       5. The method of  claim 3 , wherein longitudinal waves and transverse waves are used as ultrasound modes. 
     
     
       6. The method of  claim 1 , wherein the homogenization process prior to the forming comprises a heat treatment and/or a mechanical alignment process. 
     
     
       7. The method of  claim 1 , wherein the deviations of the measurement values are used for an open loop or closed loop process control. 
     
     
       8. The method of  claim 1 , further comprising readjusting process parameters for at least one of forming the strip, welding of the open seam tube, and a calibration or alignment processes subsequent to the welding as a function of the deviation of the measurement values. 
     
     
       9. The method of  claim 1 , wherein the nondestructive testing is carried out in an automated manner. 
     
     
       10. The method of  claim 1 , wherein the material properties are determined on the tube during individual steps of producing the tube and are used for adjusting process parameters of process steps respectively subsequent to the individual steps. 
     
     
       11. The method of  claim 1 , wherein the characteristic integral value of the material property determined on the strip or the metal sheet is used for adjusting rolling parameters of subsequently rolled strips or metal sheets.